A&A Supplement series, Vol. 129, April II, 337-341
Received June 12; accepted September 29, 1997
S. Harder - C. Bertout - C. Mennessier
Send offprint request: S. Harder
Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, BP. 53, 38041 Grenoble Cedex 9, France
Institut d'Astrophysique de Paris, 98 bis boulevard Arago, 75014 Paris, France
Photometric UBVRI observations of the YYOrionis stars YYOri, SYOri, CEOri, NSOri and XXOri are presented. The luminosity of all stars is variable on a timescale of a few days. This variation is rather irregular and no periodic variability was observed in the present data sets. The V-I and V-R colors become redder when the stars become fainter, suggesting that inhomogeneous surface temperature distributions are responsible for the observed irregular variability. Two stars located in the vicinity of our program stars and observed in the same frames turned out to be variable. They were identified as V481 Ori and AO Ori. We report a periodic modulation of the V481 Ori light curve with a period of 4.9 days.
keywords: stars: pre-main sequence -- stars: activity -- stars: variables: other